The present invention relates generally to integrated circuit (IC) designs, and more particularly to a multi-state electrical fuse.
Electrical fuses are utilized by modern ICs for adjustments and repairs that are often made late in the IC fabricating process. The electrical fuse is designed to be programmed when a current flowing through the fuse exceeds a threshold, thereby causing its resistance to increase. The original and increased resistance values of the fuse can be used to represent two logic states, such as “0” and “1.” Changing the fuse logic states can therefore be utilized for circuit adjustments and repairs.
Conventionally, the electrical fuse is designed to have only two states, programmed or not programmed. One drawback of the two-state electrical fuse is the layout inefficiency. As each fuse can only be programmed to represent a bit of data, a number of electrical fuses are needed for representing a corresponding number of bits. For example, eight electrical fuses are needed to represent a byte of data. Thus, a great number of electrical fuses are needed when a great number of data are needed to be programmed for circuit adjustments and repairs. These electrical fuses occupy a great amount of layout area, which becomes increasingly limited as the modern IC continues to shrink in size.
As such, desirable in the art of IC design is an electrical fuse that can be programmed to represent more than one bit of data in order for reducing the total number of fuses that need to be implemented in an IC.